Method of treating phosphate coatings on metal surfaces



D. L. MILES Nov. 19; 1957 METHOD OF TREATING PHOSPHATE COATINGS ON METAL SURFACES Filed July 26, 1955 JQ Q lllllllllllll United METHOD OF TREATING PHOSPHATE COATINGS N METAL SURFACES Application July 26, 1955, Serial No. 524,512

2 Claims. (Cl. 1486.15)

This invention relates to the art of preparing a succession of articles for the reception of a final siccative finish such as paint, varnish, enamel, japan or the like, and is particularly concerned with articles which have been treated to produce thereon a crystalline phosphate coating as a base for the siccative finish.

The technique of phosphate coating a succession of metal surfaces is now very old and extremely well known to those skilled in this art but, by way of background, it is desired to point out that, after the production of the phosphate coating it is generally customary to treat the phosphate coating with a dilute acidulated solution of chromic and/or phosphoric acid before applying the siccative finish. A familiar solution of this type consists of from one-half /2) to eight (8) pounds of chromic acid dissolved in 100 gallons of water. Occasionally, phosphoric acid is substituted in part for the chromic acid. In the description which follows it is to be understood that all references to treating solution refer specifically to such dilute acidulated solutions of chromic and/ or phosphoric acid.

As is well known in the art, such solutions tend to markedly decrease blistering of the siccative finish as well as to increase its adhesion. However, the results attained in this regard are not always satisfactory and I have discovered that this is due to the presence of dissolved salts other than the desired active constitutents of the solution, namely, chromic and/ or phosphoric acids. Such salts may occur as contaminations in the water employed and they also accumulate during the rinsing techniques which have so far been employed, especially where the rinsing solution is applied as a spray in the spraying systems familiar to the art where the run-off is collected and returned to the rinsing bath for re-use. Quite naturally, as a succession of phosphate coated surfaces are treated, certain contaminations in the form of soluble salts are constantly being introduced.

Heretofore, the art has endeavored to avoid this difficulty by frequently draining from the reservoir which holds the body of the treating solution, all or a portion of the solution and replenishing the volume withdrawn with new or virgin treating solution. Obviously, however, the entire bath cannot be discarded each time that it contacts a phosphated surface so that, for the greater percentage of the time that the solution is in operation, it always contains a certain amount of contamination.

With the foregoing in mind, the principal object of my invention will be better understood and it involves the provision of a rinsing technique by means of which the adhesion of the final siccative finish is greatly improved. A further object of the invention is to prevent the occurrence of blisters in the siccative finish, especially in situations where such finishes are exposed to humid atmospheres such as are encountered near the seashore or the like.

I have discovered that the effectiveness of these rinsing or treating solutions in the treatment of a succession of atent O pieces, especially where the solution is applied by means of spraying or flowing it over the phosphate coated work, is greatly increased if the last treating solution to touch the surface of the work is always new or virgin solution. By new or virgin solution I mean rinsing solution which has not been used previously in the treatment of a phosphate coated surface. For best results, this is necessary even in situations where the customary controls are applied to the body of the treating solution in order to maintain its substantial purity. Thus, even in situations where the concentration of dragged in soluble salts is kept at a minimum by frequent renewal of the solution, yet best results are not secured unless the final treating solution to touch the surface of the work is new or virgin solution.

The accompanying drawing is a diagrammatic illustration of a portion of a spraying system of the type which is familiar to those skilled in this art but which has been modified to incorporate the improvement of the present invention.

The ideal adaptation of the present invention is in a spray system and, in the accompanying drawing, I have illustrated a portion of a spraying tunnel.

The articles to be sprayed move through the tunnel in the direction indicated by the arrows 1. As the articles enter the section A of the tunnel, they have already been phosphate coated but the phosphatizing portion of the tunnel is not illustrated because in and of itself it forms no part of the present invention. In the section A the phosphate coated articles are rinsed with a treating solution constituted as described above, namely, a dilute acidulated solution of chromic and/or phosphoric acid. The reservoir for the treating solution is shown at 2 and a pump 3 driven by a motor 4 withdraws the solution from the reservoir and delivers it through the pipe 5 to the spray distribution system 6. The articles under treatment pass through this spray and the run-off is collected in the reservoir 2 in a manner well understood in this art.

The articles then continue through the tunnel to the final spraying section or station E and it should be noted that there is a relatively long section C intermediate the section A and the section B which, in the present installation, will be referred to as a drain section. The floor of sections B and C, shown in dash lines at 7, is sloped toward the reservoir 2 so that the run-off from section B will be delivered to the main body of the rinsing solution in the reservoir. The reason for the length of the drain section C is to prevent any over-spray from section A mixing with the solution sprayed in section B. This is very important because the benefits of the invention cannot be realized unless the solution sprayed in section B is strictly virgin solution.

To provide section B with virgin solution, a smaller reservoir 8 of concentrated solution is provided. Concentrated solution is withdrawn from this reservoir by means of another pump 9 and delivered through the pipe 10 to a fresh water storage tank 11 which is constantly supplied with fresh pure water through the pipe 12. The fresh virgin treating solution as mixed in the reservoir 11 is withdrawn by the pump 13 under the influence of the motor 13a and delivered through pipe 14 to the spraying elements 15 in section B. A re-circulating line 16, a pressure gauge 17, and a pressure control switch 18, are provided on the line 14 for purposes which are not impor tant insofar as the present invention is concerned so they will not be further described. Suflice it to say that by the arrangement shown, the final treating or rinsing solution to touch the surface of each phosphate coated article is always fresh or virgin solution. After treatment with this fresh solution the pieces are dried and heating may be employed to facilitate drying, if desired, following which the siccative finish can be applied.

It willbe seen that my method or technique of rinsing or treating the phosphate coated surfaces always insures that the final solution totouch the surface of the work is virgin solution while, at the same time, economy of chemical consumption is insured and the results attained in the initial rinsing stage of section A are likewise improved because of the constant replenishment of the solution in reservoir A with the relatively fresh solution which drips from the work in section B. Insection B the solution has only once touched the work'and can be added to the reservoir 2 without introducing a serious degree of contamination.

I claim: p a

1. In the art ofp'reparingajsuccession ofmetal articles for the reception of a siccative-fini'sh where the surface of the articles is first provided with a phosphate coating,

the method of successively treating the phosphate coated articles initially with a dilute-rinsing solution consisting essentially ofacid from the class consisting of chromic and phosphoric acids, thereafter treating each' article so rinsed onlywith virgin, uncontaminated rinsing solution as a final rinsing step, collecting the run-off rinsingsolution from said final virgin rinsing step anddelivering it as replenishment to the initial rinsing solution, and drying the articles after treatment with the final virgin rinsing solution.

2. In a multi-stage, spray-type, phosphating system in which a plurality of metal articles are passed in succession through a tunnel having a series of spraying stations including at least a phosphating station and a following station where the phosphate coated articles are treated with a dilute rinsing solution consisting essentially of acid from the class which consists of chromic acid and phosphoric acid and in which run-01f from each of said stations is returned to the said station; the method which includes adding to such a system a final rinsing station which sprays on the work only virgin, uncontaminated rinsing solution of the class defined, collecting the run-oft from said final rinsing station and delivering such collected run-off as replenishment to said first mentioned rinsing station.

References'Cited in the file of this patent UNITED STATES PATENTS Great Britain Apr. 22, 1942 

1. IN THE ART OF PREPARING A SUCCESSION OF METAL ARTICLES FOR THE RECEPTION OF A SICCATIVE FINISH WHERE THE SURFACE OF THE ARTICLES IS FIRST PROVIDED WITH A PHOSPHATE COATING, THE METHOD OF SUCCESSIVELY TREATING THE PHOSPHATE COATED ARTICLES INITIALLY WITH A DILUTE RINSING SOLUTION CONSISTING ESSENTIALLY OF ACID FROM THE CLASS CONSISTING OF CHROMIC AND PHOSPHORIC ACIDS, THEREAFTER TREATING EACH ARTICLE SO 